1. Field of the Invention
This invention relates to a tool for a street milling, coal-cutting, mining machine or the like which has a chisel with a chisel head and a chisel shaft. The chisel shaft is rotatably mounted in a receiver of a chisel holder. A perforated wear protection element is mounted on the chisel head with the chisel head sitting closely on the chisel holder with the wear protection element interposed.
2. Description of Related Art
A tool is known from European Patent Reference EP 0 413 917 A1, where the wear protection element is formed as a circular steel sheet disk, from which an opening is punched in the center. The opening is extended in the direction of the chisel head. A chamfered part of the chisel head lies in this extension. The wear protection element lies flat on a contact surface of the chisel holder. During use of the tool, waste material can get past the chisel head and the wear protection element and reach the receiver. In this position, this material can block the free rotation of the chisel.
Another tool for mounting a chisel on a chisel holder is known from European Patent Reference EP 0 200 37 B1, where the chisel head is set directly on the chisel holder. The chisel holder is designed to be under spring tension on a base part that can be attached on its side to a milling roller. The chisel can also become fixed due to waste material penetrating into the receiver, and then the chisel can no longer rotate freely.
One object of this invention is to provide a tool of the above mentioned type, which has good wear behavior.
The wear protection element comprises one or more spring elements that elastically support the chisel head relative to the chisel holder.
Due to the spring-tensioned support of the chisel head, intermittent forces acting on the chisel are damped so that excessive material stresses are prevented. In addition, the spring force provides an axial play for the chisel, wherein the chisel head can then also move axially in the receiver of the chisel holder. With this axial play, there is a type of xe2x80x9cpump effectxe2x80x9d which can extract waste material that has reached the region of the receiver. Thus, the free rotation of the chisel can be maintained.
In order to keep the cost of parts and assembly to a minimum, according to a preferred embodiment of this invention, spring elements are formed integrally with the wear element.
In one possible embodiment of this invention, the wear protection element comprises a base part with at least one flat contact surface that contacts an opposing surface of the chisel head or the chisel holder. A circumferential section acting as a spring element is bent in the direction of the chisel holder or the chisel head from the base part. The spring element supports the chisel holder or the chisel head on the region of the spring element facing away from the base part.
However, it is also conceivable for several, preferably three, spring elements that are separated from each other to be bent from the base part. With these spring elements, a definite, statically determinate support situation is achieved.
In order to be able to achieve progressive or regressive spring characteristics, according to one embodiment of this invention, each spring element comprises two or more spring sections that exhibit different spring rigidity and/or the same or different spring deflections.
A tool according to this invention has an area around the opening in which the chisel shaft is inserted, with a circumferential centering attachment that projects in the direction of the chisel holder and that interacts with a centering extension of the receiver of the chisel holder. The centering extension of the chisel holder simplifies assembly of the chisel shaft in the receiver. During operation, the region of the contact surface on which the wear protection element is supported and which is arranged around the receiver gradually wears away. This is caused by rotation of the wear protection element on this contact surface. With a centering attachment at the wear protection element, the centering extension is worn away to the same degree as the contact surface. However, this causes the centering extension to remain in place.
A tool with a simple configuration and that is cost-effective to produce is obtained according to this invention when the wear element is produced as a stamped, bent part from a flat material blank, from which the opening for the chisel shaft is punched and whose edge or edges are bent for completely or partially forming the spring elements.
Here, one or more reinforcing ribs can be formed on the edges that form the spring elements. The reinforcing ribs increase the spring rigidity. Thus, a relatively low material strength can be used for the wear protection element yet still provide a high spring rate.